Nearly all Western nations have, over the past couple decades, added anti-counterfeiting measures to their currency. One popular mechanism currently in use in many nations is a small strip with holograms on it; reproducing holograms has historically been much more complex and expensive for criminals versus printing bogus copies of equivalent currency that did not sport holograms.
What is the scam? How do crooks defeat holograms?
Now, however, a simple method of impersonating holograms has surfaced - and it is tricking unsuspecting people. The Royal Canadian Mounted Police warn that criminals are cutting the hologram strip (which, in Canada, is a clear plastic-looking strip that contains holograms) off of smaller denomination bills - in Canada's case the $5 Bill is the lowest denomination of paper money - and adding them to counterfeit larger bills. In order not to lose the $5 bills the crooks replace the holograms on those bills with aluminum foil and tape, making crude copies of what was the original bill. People generally do not check smaller bills even for obvious signs of counterfeiting - criminals know this, and are exploiting this human weakness. (CTV News even showed the foil-doctored bills to Canadians on the street and most of the folks who were shown the bill admitted that they would not have noticed anything amiss if they had been handed the $5 bill from someone else.)
What do you need to do?
When you receive a piece of currency - regardless of the denomination - always take a quick look to make sure that it looks legitimate. Look at more than one security feature - it takes less than a second. For US Currency features please see the Federal Reserve website.
Also, check the hologram: Holograms on Canada's $5 bill have tiny 5s are across the front and back of the panel, feature Sir Wilfrid Laurier at the top, and the Parliament tower at the bottom. The holograms on Canada's other bills have different numbers, and feature different people and different Canadian buildings. A $100 bill should not have the hologram from a $5 bill.
Additionally, governments should consider making holograms and their corresponding strips as different as possible for different denominations - shape (preferably irregular), size, placement on the bill, etc. so that the incorrect hologram for a denomination will stand out as much as possible. Larger denominations should also have larger holograms - making it difficult for criminals to cut and shape holograms from smaller denominations for larger bills.